GUI: don't crash / hang on certain environments if accessibility support is enabled

GUI: fixed various issues in Unscaled HiDPI Output mode

GUI: extend the VM Input menu with Print Screen-related actions

GUI: improved handling of inserting the Guest Additions ISO image by trying all available optical drives rather than only the first one and by not asking the user if he wants to force unmounting (which doesn't work in most cases anyway)

API: default to RTC using UTC for Solaris 11 guests

Settings: be less restrictive when reading a VM configuration containing a host-only adapter without an interface name